Characterization and activity of sonochemically-prepared BSA microspheres containing Taxol--an anticancer drug

Biopolymer Lipid Hybrid Microcarrier for Transmembrane Inner Ear Delivery of Dexamethasone

Dexamethasone is one of the most often used corticosteroid drugs for sensorineural hearing loss treatment, and is used either by intratympanic injection or through systemic delivery. In this study, a biopolymer lipid hybrid microcarrier was investigated for enhanced local drug delivery and sustained release at the round window membrane level of the middle ear for the treatment of sensorineural hearing loss (SNHL). Dexamethasone-loaded and dexamethasone-free microparticles were prepared using biopolymers (polysaccharide and protein, pectin and bovine serum albumin, respectively) combined with lipid components (phosphatidylcholine and Dimethyldioctadecylammonium bromide) in order to obtain a biopolymer–liposome hybrid system, with a complex structure combining to enhance performance in terms of physical and chemical stability. The structure of the microparticles was evaluated by FTIR, XRD, thermal analysis, optical microscopy, and scanning electron microscopy (SEM). The encapsulation efficiency determination and the in vitro Dexamethasone release study were performed using UV-Vis spectroscopy. The high value of encapsulation efficiency and the results of the release study indicated six days of sustained release, encouraging us to evaluate the in vitro cytotoxicity of Dexamethasone-loaded microparticles and their influence on the cytotoxicity induced by Cisplatin on auditory HEI-OC1 cells. The results show that the new particles are able to protect the inner ear sensory cells.

Update of ultrasound-assembling fabrication and biomedical applications for heterogeneous polymer composites

As a power-driving approach, ultrasound irradiation is very appealing to the preparation or modification of new materials. In the review, we overviewed the latest development of ultrasound-mediated effects or reactions in polymer composites, and demonstrated its unique and powerful aspects on the polymerization or aggregation. The review generalized the different categories of heterogeneous polymer composites by defining the constituents, and described the shapes, sizes and basic properties of various purpose-specific or site-specific products. Importantly, the review paid more attention to the main biomedicine applications of heterogeneous polymer composites, such as drug or bioactive substance entrapment, delivery, release, imaging, and therapy, and emphasized many advantages of ultrasound-assembling approaches and heterogeneous polymer composites in biology and medicine fields. In addition, the review also indicated the prospective challenges of heterogeneous polymer composites both in ultrasound-assembling designs and in biomedical applications.

Characterization of sonochemically prepared human serum albumin nanocapsules using different plant oils as core component for targeted drug delivery

The focus of this study is the preparation of proteinaceous human serum albumin (HSA) nanocapsules with biocompatible plant oil cores avoiding toxic cross-linker and noxious non-aqueous liquids. The sonochemical preparation of HSA capsules with different plant oils yields particles with narrow size distribution forming suspensions stable for at least 14 days and enabling long-term storage by freezing. Furthermore, wheat germ agglutinin (WGA) as a targeting molecule was successfully embedded into the proteinaceous particle shell at a molar ratio of 7:1 (HSA/WGA). As urothelial cell binding studies revealed up to 55% higher cell binding potential of WGA-grafted particles than those without a targeter, targeted protein nanocapsules represent the first step towards new and innovative formulations.

Scalable fabrication of tunable titanium nanotubes via sonoelectrochemical process for biomedical applications

Titanium does not react well with the human tissues and due to its bio-inert nature the surface modification has yet to be well-studied. In this study, the sonoelectrochemical process has been carried out to generate TiO₂ nanotube arrays on implantable Ti 6-4. All the prepared nanotubes fill with the vancomycin by immersion and electrophoresis method. Drug-releasing properties, antibacterial behavior, protein adsorption and cell attachment of drug-modified nanotubes are examined by UV-vis, flow cytometry, modified disc diffusion, BSA adsorption, and FESEM, respectively. The most uniform morphology, appropriate drug release, cell viability behavior and antibacterial properties can be achieved by samples anodized in the range of 60-75 V. Also improves the adsorption of BSA protein in bone healing and promotes osteoblast activity and osseointegration. Drug loading efficiency increases up to 60% via electrophoresis comparing the immersion method for anodized sample in 75 V. While electrophoresis does not affect the amount of vancomycin adsorption for lower voltages. Besides, the present study indicates that an anodized sample without drug loading has no antibacterial activity. Moreover, 28-days drug releasing from nanotubes is investigated by mathematical formula according to Fickian's law to find an effective dose of loaded drug.

Characterization of Magnetic Nanoparticle-Seeded Microspheres for Magnetomotive and Multimodal Imaging

Magnetic iron-oxide nanoparticles have been developed as contrast agents in magnetic resonance imaging (MRI) and as therapeutic agents in magnetic hyperthermia. They have also recently been demonstrated as contrast and elastography agents in magnetomotive optical coherence tomography and elastography (MM-OCT and MM-OCE, respectively). Protein-shell microspheres containing suspensions of these magnetic nanoparticles in lipid cores, and with functionalized outer shells for specific targeting, have also been demonstrated as efficient contrast agents for imaging modalities such as MM-OCT and MRI, and can be easily modified for other modalities such as ultrasound, fluorescence, and luminescence imaging. By leveraging the benefits of these various imaging modalities with the use of only a single agent, a magnetic microsphere, it becomes possible to use a widefield imaging method (such as MRI or small animal fluorescence imaging) to initially locate the agent, and then use MM-OCT to obtain dynamic contrast images with cellular level morphological resolution. In addition to multimodal contrast-enhanced imaging, these microspheres could serve as drug carriers for targeted delivery under image guidance. Although the preparation and surface modifications of protein microspheres containing iron oxide nanoparticles has been previously described and feasibility studies conducted, many questions regarding their production and properties remain. Since the use of multifunctional microspheres could have high clinical relevance, here we report a detailed characterization of their properties and behavior in different environments to highlight their versatility. The work presented here is an effort for the development and optimization of nanoparticle-based microspheres as multi-modal contrast agents that can bridge imaging modalities on different size scales, especially for their use in MM-OCT and MRI imaging.

Preparation of meglumine antimonate loaded albumin nanoparticles and evaluation of its anti-leishmanial activity: an in vitro assay

Cutaneous leishmaniasis is still a health problem worldwide, especially in tropical and subtropical areas. Currently, pentavalent antimony compounds are used to treat leishmaniasis. These compounds cause various side effects in the body. Therefore, there is a need to discover new drugs with less toxicity and more therapeutic effects. In this study, we encapsulated the meglumine antimonate into the albumin as a drug carrier and evaluated the anti-leishmanial effect of the prepared nanoparticles. The precipitation method was used for this purpose by applying different concentrations of glutaraldehyde and N-(3-Dimethylaminopropyl)-N-ethyl carbodiimide hydro chloride Ethyl (DEC) and then, field emission test was performed using Scanning Electron Microscopy for evaluating the morphology and size particles. The cytotoxicity and inhibitory of drugs were evaluated on J774 macrophages and Leishmania major promastigotes, respectively. Nanodrugs prepared using glutaraldehyde (10 μl/ml) and DEC (13 mg/ml) had the smallest and largest size, respectively. The highest anti-leishmanial activity was observed in the drugs prepared with glutaraldehyde (10 μl/ml). Also this nanodrug had the lowest cytotoxicity against macrophages. Given that meglumine antimonate loaded albumin nanoparticles prepared with glutaraldehyde (10 μg/ml), can improve the anti-leishmanial effects of this old drug, it can be a good option as a drug delivery system.

Sonochemistry-Assembled Stimuli-Responsive Polymer Microcapsules for Drug Delivery

Stimuli-responsive polymer microcapsules (PMs) fabricated by the sonochemical method have emerged for developing useful drug delivery systems, and the latest developments are mainly focusing on the synthetic strategies and properties such as structure, size, stability, loading capacity, drug delivery, and release. There, the primary attribution of sonochemistry is to offer a simple and practical approach for the preparation of PMs. Structure, size, stability, and properties of PMs are designed mainly according to synthetic materials, implementation schemes, or specific demands. Numerous functionalities of PMs based on different stimuli are demonstrated: targeting motion in a magnetic field or adhering to the living cells with sensitive sites through molecular recognition, and stimuli-triggered release including enzymatic catalysis, chemical reaction as well as physical or mechanical process. The current review discusses the basic principles and mechanisms of stimuli effects, and describes the progress in the application such as targeted drug systems and controlled drug systems, and also gives an outlook on the future challenges and opportunities for drug delivery and theranostics.

Proteinaceous microspheres as a delivery system for carvacrol and thymol in antibacterial applications

There is an urgent need for new materials with antimicrobial activity. Phenolic essential oil (EO) compounds with Generally Recognized As Safe (GRAS) status are attractive candidates, but they need suitable delivery systems to overcome specific drawbacks. Core-shell microspheres (MSs) of Bovine Serum Albumin (BSA) or Human Serum Albumin (HSA) encapsulating such active compounds in the oil phase are a delivery system that is novel in combination with phenolic EO compounds. Moreover, the EO compounds can also be assembled in an oil shell around a protein core by choosing an appropriate oil phase. A facile sonochemical fabrication method, which can be easily scaled-up, is developed with full characterization of the resulting EO-containing MSs by optical and electron microscopy. Bacterial growth experiments with E. coli including TEM of treated cells confirm antibacterial activity. In the case of carvacrol, the corresponding MSs are found to be both more bioactive and more stable than the free biocide.

Sonochemical synthesis, characterization, and effects of temperature, power ultrasound and reaction time on the morphological properties of two new nanostructured mercury(II) coordination supramolecule compounds

Two new mercury(II) coordination supramolecular compounds (CSCs) (1D and 0D), [Hg(L)(I)₂]_n (1) and [Hg₂(L')₂(SCN)₂]·2H₂O (2) (L=2-amino-4-methylpyridine and L'=2,6-pyridinedicarboxlic acid), have been synthesized under different experimental conditions. Micrometric crystals (bulk) or nano-sized materials have been obtained depending on using the branch tube method or sonochemical irradiation. All materials have been characterized by field emission scanning electron microscope (FESEM), scanning electron microscopy (SEM), powder X-ray diffraction (PXRD) and FT-IR spectroscopy. Single crystal X-ray analyses on compounds 1 and 2 show that Hg²⁺ ions are 4-coordinated and 5-coordinated, respectively. Topological analysis shows that the compound 1 and 2 have 2C1, sql net. The thermal stability of compounds 1 and 2 in bulk and nano-size has been studied by thermal gravimetric (TG), differential thermal analyses (DTA) for 1 and differential scanning calorimetry (DSC) for 2, respectively. Also, by changing counter ions were obtained various structures 1 and 2 (1D and 0D, respectively). The role of different parameters like power of ultrasound irradiation, reaction time and temperature on the growth and morphology of the nano-structures are studied. Results suggest that increasing power ultrasound irradiation and temperature together with reducing reaction time and concentration of initial reagents leads to a decrease in particle size.

Intravascular magnetomotive optical coherence tomography of targeted early-stage atherosclerotic changes in ex vivo hyperlipidemic rabbit aortas

We report the development of an intravascular magnetomotive optical coherence tomography (IV-MM-OCT) system used with targeted protein microspheres to detect early-stage atherosclerotic fatty streaks/plaques. Magnetic microspheres (MSs) were injected in vivo in rabbits, and after 30 minutes of in vivo circulation, excised ex vivo rabbit aorta samples specimens were then imaged ex vivo with our prototype IV-MM-OCT system. The alternating magnetic field gradient was provided by a unique pair of external custom-built electromagnetic coils that modulated the targeted magnetic MSs. The results showed a statistically significant MM-OCT signal from the aorta samples specimens injected with targeted MSs.

Curcumin delivered through bovine serum albumin/polysaccharides multilayered microcapsules

The aim of the paper is to obtain and characterize k-carrageenan–chitosan dual hydrogel multilayers shell BSA gel microcapsules, as a carrier for curcumin, and as a possible antitumoral agent in biological studies. We used the CaCO3 template to synthesize non-toxic CaCO3/BSA particles as microtemplates by coprecipitating a CaCl2 solution that contains dissolved BSA, with an equimolar Na2CO3 solution. The microcapsules shell is assembled through a layer-by-layer deposition technique of calcium cross-linked k-carrageenan hydrogel alternating with polyelectrolite complex hydrogel formed via electrostatic interactions between k-carrageenan and chitosan. After the removal of CaCO3 through Ca2+ complexation with EDTA, and by a slightly treatment with HCl diluted solution, the BSA core is turned into a BSA gel through a thermal treatment. The BSA gel microcapsules were then loaded with curcumin, through a diffusion process from curcumin ethanolic solution. All the synthesized particles and microcapsules were stucturally characterized by: Fourier Transform Infrared Spectroscopy, UV–Vis Spectrometry, X-ray diffraction, thermal analysis, fluorescence spectroscopy, fluorescence optical microscopy, confocal laser scanning microscopy and scanning electron microscopy. The behavior of curcumin loaded microcapsules in media of different pH (SGF, SIF and PBS) was studied in order to reveal the kinetics and the release profile of curcumin. The in vitro evaluation of the antitumoral activity of encapsulated curcumin microcapsules on HeLa cell line and the primary culture of mesenchymal stem cells is the main reason of the microcapsules synthesis as BSA-based vehicle meant to enhance the biodisponibility of curcumin, whose anti-tumor, anti-oxidant and anti-inflammatory properties are well known.

Magnetomotive optical coherence tomography for the assessment of atherosclerotic lesions using αvβ3 integrin-targeted microspheres

PURPOSE

We investigated the early-stage fatty streaks/plaques detection using magnetomotive optical coherence tomography (MM-OCT) in conjunction with αvβ3 integrin-targeted magnetic microspheres (MSs). The targeting of functionalized MSs was investigated by perfusing ex vivo aortas from an atherosclerotic rabbit model in a custom-designed flow chamber at physiologically relevant pulsatile flow rates and pressures.

PROCEDURES

Aortas were extracted and placed in a flow chamber. Magnetic MS contrast agents were perfused through the aortas and MM-OCT, fluorescence confocal, and bright field microscopy were performed on the ex vivo aorta specimens for localizing the MSs.

RESULTS

The results showed a statistically significant and stronger MM-OCT signal (3.30 ± 1.73 dB) from the aorta segment perfused with targeted MSs, compared with the nontargeted MSs (1.18 ± 0.94 dB) and control (0.78 ± 0.41 dB) aortas. In addition, there was a good co-registration of MM-OCT signals with confocal microscopy.

CONCLUSIONS

Early-stage fatty streaks/plaques have been successfully detected using MM-OCT in conjunction with αvβ3 integrin-targeted magnetic MSs.

Sono-assembly of highly biocompatible polysaccharide capsules for hydrophobic drug delivery

Cells like sugar. General synthesis and potential of intracellular hydrophobic drug delivery of single-component polysaccharide capsules are pursued. The capsules can be generally assembled through hydrogen bonding networks but show striking shell robustness. The evidenced cell internalization, stimuli-responsiveness to local pH changes and high biocompatibilities of the capsules specifically favor their potential intracellular drug delivery.

A comparison of the physical properties of ultrasonically synthesized lysozyme- and BSA-shelled microbubbles

Ultrasonic technique has been used for synthesising protein microspheres possessing specific physical and functional properties. Various proteins have been used as shell materials under different experimental conditions. In previous studies, thermal or chemical denaturation of the proteins was used to obtain stable bovine-serum albumin (BSA) and lysozyme microbubbles (MBs), respectively. It is ideal to establish a generic procedure to synthesise microspheres irrespective of the nature of the protein. In order to see if a generic procedure can be established, ultrasonic synthesis of lysozyme and BSA MBs was carried out under similar experimental conditions and their properties were evaluated. The size, size distribution and the stability of the MBs were significantly different for the lysozyme and BSA MBs. The size and size distribution of the lysozyme coated MBs were larger than BSA bubbles. The mechanical strength of MBs against the shear forces, generated when irradiated by high frequency ultrasound, was studied using pulsed-sonoluminescence (SL). This study indicated that lysozyme MBs were significantly more stable than BSA MBs. An increase in mechanical strength of the MBs may lead to an increase in their storage lifetime and stability against gas diffusion. Possible reasons for such observations have been discussed.

Estimating the delivery efficiency of drug-loaded microbubbles in cancer cells with ultrasound and bioluminescence imaging

The application of drug-loaded microbubbles (MBs) in combination with ultrasound (US), which results in an increase in capillary permeability at the site of US-sonication-induced MB destruction, may be an efficient method of localized drug delivery. This study investigated the mechanism underlying the US-mediated release of luciferin-loaded MBs through the blood vessels to targeted cells using an in vivo bioluminescence imaging (BLI) system. The luciferin-loaded MBs comprised an albumin shell with a diameter of 1234 ± 394 nm (mean ± SD) and contained 2.48 × 10⁹ bubbles/mL; within each MB, the concentration of encapsulated luciferin was 1.48 × 10⁻¹⁰ mg/bubble. The loading efficiency of luciferin in MBs was only about 19.8%, while maintaining both the bioluminescence and acoustic properties. In vitro and in vivo BLI experiments were performed to evaluate the US-mediated release of luciferin-loaded MBs. For in vitro results, the increase in light emission of luciferin-loaded albumin-shelled MBs after destruction via US sonication (6.24 ± 0.72 × 10⁷ photons/s) was significantly higher than that in the luciferin-loaded albumin-shelled MBs (3.11 ± 0.33 × 10⁷ photons/s) (p < 0.05). The efficiency of the US-mediated release of luciferin-loaded MBs in 4T1-luc2 tumor-bearing mice was also estimated. The signal intensity of the tumor with US destruction at 3 W/cm² for 30 s was significantly higher than without US destruction at 3 (p = 0.025), 5 (p = 0.013), 7 (p = 0.012) and 10 (p = 0.032) min after injecting luciferin-loaded albumin-shelled MBs. The delivery efficiency was, thus, improved with US-mediated release, allowing reduction of the total injection dose of luciferin.

Confinement of Acoustic Cavitation for the Synthesis of Protein-Shelled Nanobubbles for Diagnostics and Nucleic Acid Delivery

We report a novel flow-through sonication technique for synthesizing stable and monodispersed nano- and micrometer-sized bubbles that have potential applications in diagnostics and gene therapy. The size and size distribution of the bubbles are controlled by the active cavitation zone generated by ultrasound. These bubbles are shown to possess echogenic properties and can be used for loading oligonucleotides.

Fragrance release profile from sonochemically prepared protein microsphere containers

Protein microspheres have been prepared by sonicating a mixture of pure fragrant oil (amyl acetate (AA)) with an aqueous protein (bovine serum albumin) solution. The prepared protein spheres are nano- to micrometer sized with an encapsulation efficiency of approx. 97% for the AA present on the surface and inside the BSA capsule. Containers were found stable for more than 6 months when stored sealed at 4°C and 20°C. For the release profile measurements, we used a simple, automated and direct method. We continuously weighed the encapsulated microspheres and measured the evaporation rates. The release profiles at 15°C and 25°C display two different evaporation rates. The higher rate is the sum of a few evaporation rates, including water molecules, while the slower rate is due to the evaporation of pure AA. The changes in the evaporation rates occur upon the collapse of the container. This event coincides with the full evaporation of water. For morphological characterization we dyed the AA with Nile red, and used SEM, ESEM, Cryo-SEM, light microscopy, and confocal laser scanning microscopy measurements.

Surface-modified protein microspheres capture amyloid-β and inhibit its aggregation and toxicity

The biocompatible and biodegradable properties of protein microspheres and the recent advances in their preparation have generated considerable interest of utilizing these core-shell structures for drug delivery and diagnostic applications. However, effective targeting of protein microspheres to desirable cells or loci still remains a challenge. Here, we describe for the first time a facile one-pot sonochemical approach for covalent modification of protein microspheres made from serum albumin; the surface of which is covalently decorated with a short recognition peptide to target amyloid-β (Aβ) as the main pathogenic protein in Alzheimer's disease (AD). The microspheres were characterized for their morphology, size, and entrapment efficacy by electron microscopy, dynamic light scattering and confocal microscopy. Fluorescence-activated cell-sorting analysis and Thioflavin-T binding assay demonstrated that the conjugated microspheres bind with high affinity and selectivity to Aβ, sequester it from the medium and reduce its aggregation. Upon incubation with Aβ, the microspheres induced formation of amorphous aggregates on their surface with no apparent fibrillar structure. Moreover, the microspheres directly reduced the Aβ-induced toxicity toward neuron like PC12 cells. The conjugated microspheres are smaller than unmodified microspheres and remained stable throughout the incubation under physiological conditions.

Sonochemically born proteinaceous micro- and nanocapsules

The use of proteins as a substrate in the fabrication of micro- and nanoparticulate systems has attracted the interest of scientists, manufactures, and consumers. Albumin-derived particles were commercialized as contrast agents or anticancer therapeutics. Food proteins are widely used in formulated dietary products. The potential benefits of proteinaceous micro- and nanoparticles in a wide range of biomedical applications are indisputable. Protein-based particles are highly biocompatible and biodegradable structures that can impart bioadhesive properties or mediate particle uptake by specific interactions with the target cells. Currently, protein microparticles are engineered as vehicles for covalent attachment and/or encapsulation of bioactive compounds, contrast agents for magnetic resonance imaging, thermometric and oximetric imaging, sonography and optical coherence tomography, etc. Ultrasound irradiation is a versatile technique which is widely used in many and different fields as biology, biochemistry, dentistry, geography, geology, medicine, etc. It is generally recognized as an environmental friendly, cost-effective method which is easy to be scaled up. Currently, it is mainly applied for homogenization, drilling, cleaning, etc. in industry, as well for noninvasive scanning of the human body, treatment of muscle strains, dissolution of blood clots, and cancer therapy. Proteinaceous micro- and nanocapsules could be easily produced in a one-step process by applying ultrasound to an aqueous protein solution. The origin of this process is in the chemical changes, for example, sulfhydryl groups oxidation, that takes place as a result of acoustically generated cavitation. Partial denaturation of the protein most probably occurs which makes the hydrophobic interactions dominant and also responsible for the formation of stable capsules. This chapter aims to present the current state-of-the-art in the field of sonochemically produced protein micro- and nanocapsules, paying special attention to the proposed mechanisms for their formation, the factors that influence the capsules characteristics as well to the current applications of these particles. Current challenges in the field are also outlined as, for example, the ultrasound-protein interaction and other possible aspects of the mechanism of their formation.

Engineered biological entities for drug delivery and gene therapy protein nanoparticles

The development of genetic engineering techniques has speeded up the growth of the biotechnological industry, resulting in a significant increase in the number of recombinant protein products on the market. The deep knowledge of protein function, structure, biological interactions, and the possibility to design new polypeptides with desired biological activities have been the main factors involved in the increase of intensive research and preclinical and clinical approaches. Consequently, new biological entities with added value for innovative medicines such as increased stability, improved targeting, and reduced toxicity, among others have been obtained. Proteins are complex nanoparticles with sizes ranging from a few nanometers to a few hundred nanometers when complex supramolecular interactions occur, as for example, in viral capsids. However, even though protein production is a delicate process that imposes the use of sophisticated analytical methods and negative secondary effects have been detected in some cases as immune and inflammatory reactions, the great potential of biodegradable and tunable protein nanoparticles indicates that protein-based biotechnological products are expected to increase in the years to come.

Spatial distribution of acoustic cavitation bubbles at different ultrasound frequencies

Images of sonoluminescence, sonophotoluminescence and sonochemiluminescence are recorded in order to semi-quantitatively compare the spatial distribution of the cavitation activity at three different ultrasound frequencies (170 kHz, 440 kHz and 700 kHz) and at various acoustic amplitudes. At all ultrasound frequencies investigated, the sonochemically active cavitation zones are much larger than the cavitation zones where sonoluminescence is observed. Also, the sonochemically active bubbles are observed at relatively lower acoustic amplitudes than that required for sonoluminescence bubbles to appear. The acoustic power required for the observation of the initial cavitation bubbles increases with an increase in the ultrasound frequency. The cavitation bubbles are observed relatively uniformly throughout the reactor at 170 kHz whereas they are located away from the transducer at the higher frequencies used in this study. While these observations highlight the complexities involved in acoustic cavitation, possible reasons for the observed results are discussed.

Modeling the coupling of reaction kinetics and hydrodynamics in a collapsing cavity

We introduce a model of cavitation based on the multiphase Lattice Boltzmann method (LBM) that allows for coupling between the hydrodynamics of a collapsing cavity and supported solute chemical species. We demonstrate that this model can also be coupled to deterministic or stochastic chemical reactions. In a two-species model of chemical reactions (with a major and a minor species), the major difference observed between the deterministic and stochastic reactions takes the form of random fluctuations in concentration of the minor species. We demonstrate that advection associated with the hydrodynamics of a collapsing cavity leads to highly inhomogeneous concentration of solutes. In turn these inhomogeneities in concentration may lead to significant increase in concentration-dependent reaction rates and can result in a local enhancement in the production of minor species.